The stuff you mutter to yourself under your breath becomes your factory settings.

The offhand phrases you use about yourself do the most work, precisely because you never examine them. A deliberate belief gets questioned, while a mutter slips straight past and settles in. Repeat one often enough and it becomes the default your mind reaches for before you have consciously decided anything. Nobody else hears these, which is exactly why nobody else can correct them.

Listen for your own muttering this week, especially right after something goes wrong. Write down the exact phrase you use. Seeing it in writing is usually enough to notice how little is behind it.